The causal pathogen of tomato powdery mildew disease was identified as Leveillula taurica (Lev.) Amaud according to the symptoms and the morphological characteristics of the fungal conidiophores and conidia . Conidia often germinate at the basal or lateral sites forming uni­or multi germ tubes. Conidial germination was better on tomato leaf strips under moist atmosphere than in free water or dry conditions. Number of conidiophores and their branching depend on the susceptibility of tomato cultivar. Few uni and unbranched conidiophores in the least susceptible cv. Super strain-B and multi and occasionally branched conidiophores in the highly susceptible cv. Strain-B were observed. However, intermediate number of conidiophores and conidia formed in the lower surface of the moderately susceptible cv. Castle Rock. Examination of conidial germination revealed that spore germ tubes are initiated after 6 hr. from inoculation under warm and wet conditions and their elongation extends from 12-24 hr. towards the stomata of the upper leaf surface. Well developed symptoms appeared 7 days after inoculation under greenhouse conditions at 26°C±2 on tomato plant leaves simultaneously with that inoculated detached leaves In vitro.